Helicobacter pylori (Hp) infects the gastric mucosa of >50% of the world's population. Infection with this gram negative bacterium results in significant gastroduodenal diseases that include chronic gastritis, ulcers and cancer. Prevalence rates of Hp infection are high among underrepresented minority and lower income populations. These groups also have the highest risk of developing gastric cancer. The chronic inflammation that is a hallmark of the infection is considered a risk factor for the development of gastric cancer. Individuals infected with strains that carry the functional form of the cytotoxin-associated gene A, cagA, have an increased risk of developing gastric cancer. Hp is thus the first bacterial agent to be classified as a class I carcinogen. Since gastric cancer is the second deadliest form of cancer and delays in diagnosis contribute to poor prognosis, the detection of biomarkers that not only report the infection, but also allow detection of carcinoma development is clearly important. Since duodenal ulcer disease and gastric cancer are mutually exclusive, we hypothesize that a comparison of the proteomic profile of gastric epithelial cells of patients infected with Hp but with different diseases linked to this infection will reveal important disease-specific biomarkers of gastric cancer. To test this hypothesis we plan to address the following specific aims: Aim 1. Characterize the differences in the biomarker profile of gastric epithelial cells from patients infected with Hp who are diagnosed with gastric cancer or duodenal ulcers. The protein profile of uninfected donors will be used as a baseline control. In this aim, gastric biopsies will be used to isolate epithelial cells, whose proteins will be solubilized for profiling by high resolution two-dimensional gel electrophoresis (2-DE). Biomarkers whose expression is consistently altered in gastric cancer patients and not in duodenal ulcer patients will be identified by peptide mass fingerprinting using matrix-assisted laser desorption ionization-time-of-flight MS (MALDI-TOF- MS). Changes in expression of these proteins will be validated by western blotting with specific antibodies and confirmed by immunohistochemistry of representative tissues. Aim 2. Determine what biomarkers are induced by in vitro infection of gastric epithelial cells with Hp. In this aim, gastric epithelial cells from uninfected individuals will be infected with cagA+ strains of Hp or cagA- strains, as controls, to determine what biomarkers detected in Aim 1 are induced early in the course of infection and could thus be considered early biomarkers of cell transformation. PUBLIC HEALTH RELEVANCE: Gastric cancer is the second deadliest cancer worldwide and its linked to infection with the Helicobacter pylori bacterium. Since in its early stages gastric cancer causes no symptoms, delays in diagnosis contribute to the high mortality rate associated with this form of cancer. The objective of this project is to implement high throughput technology to identify proteins that could become candidate biomarker signatures that would aid in early diagnosis of Helicobacter pylori infection and gastric cancer development.